Real-Time Silica Discriminating Respirable Aerosol Monitor

ABSTRACT

An airborne silica detection system provides a chemiluminescence reaction for quantitative assessment of silica on an automated basis. A prefilter allows reaction to be sensitive to particle sizes relevant to chronic respiratory diseases.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of US provisional application62/654,713 filed Apr. 9, 2018 and hereby corporate by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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BACKGROUND OF THE INVENTION

The present invention relates generally to monitors for silica dust andin particular to a near-real-time monitor that can distinguish betweensilica dust and other particulate types.

Crystalline silica dust, specifically the particle size of less thanfour microns, can evade the body's natural air filtration mechanisms ofthe nose and throat to embed deep in the lungs where it can promotechronic respiratory diseases such as silicosis, lung cancer, or chronicpulmonary obstructive disease. Such dust can arise in a wide variety ofmanufacturing environments including construction and demolition, miningand quarry operations, foundries, ceramic, and stone cutting operationsand the like. For this reason, the Occupational Safety and HealthAdministration (OSHA) enforces an exposure limit to less than an averageof 50 micrograms per square meter of SiO₂ over an eight-hour period.

Typical monitoring requires collection of a sample of airborneparticulate matter using a filter for an extended period of time, forexample, 8 hours, which is often sent to a remote site for analysisusing x-ray diffraction which can identify silica. This process mayimpose time delays of many days or even weeks limiting the ability torespond promptly to the air quality conditions.

Real time monitoring of dust can be obtained, for example, by measuringscattered light, for example, from a laser, passing through an airsample. While this technique provides rapid assessment of dust, itcannot distinguish between silica dust and other dust types not coveredby the regulations and possibly presenting a lower risk. For thisreason, the readings provided by such instruments need to be adjusted byan estimate of the percentage of silica in the dust, a task that isproblematic to perform accurately in many manufacturing environments andthat can significantly affect the accuracy of the measurement.

SUMMARY OF THE INVENTION

The present invention provides an on-site, near-real-time measurement ofdust that can accurately identify respirable silica dust concentrationsto provide a more accurate measurement of exposure to respirable silica.This improved measurement speed allows prompt remedial action whenrequired while reducing or eliminating false positive measurements.

Specifically then, the present invention in one embodiment provides anairborne silica detection system having a particle sizer for receivingan airstream and preferentially removing particles greater than 4 μmaverage diameter from the airstream. A reagent tank receives theairstream downstream from the particle sizer and introduces it into a atleast one liquid reagent reacting with silica of the particles where aphotodetector monitors the reagent tank to detect a change in lightcaused by the reacting of the silica. An electronic computer executes astored program held in non-transitory computer readable medium toreceive a signal from the photo detector to provide an output indicatingsilica concentrations over a predetermined amount.

It is thus a feature of at least one embodiment of the invention toprovide an automatable method of monitoring silica exposure on an a nearreal-time basis. By providing a particle sizer, a size-indifferentchemical reaction can be used to quantitatively assess particlesrelevant to chronic respiratory diseases.

The airborne silica detection system may further include a particlegrowth chamber receiving the airstream from the particle sizer toincrease the individual mass of the particles less than 4 μm in diameterprior to receipt by the reagent tank.

It is thus a feature of at least one embodiment of the invention toimprove the sensitivity of the system to extremely fine particles whichcan be relevant to respiratory disease but which may the reagent throughpercolation out of the reagent.

The predetermined amount may be a density of silicon dioxide of lessthan 0.1 μg/m³ in the airstream or less than, for example, 40 μg /m³ or50 μg /m³ in the airstream.

It is thus a feature of at least one embodiment of the invention toprovide a system that can make measurements that comport with or exceedcurrent health standards detection requirement.

The at least one reagent provide a chemiluminescent reaction and thephotodetector may be a light sensor directed into a reagent reservoir orother mixing volume.

It is thus a feature of at least one embodiment of the invention toprovide a detection reaction eliminating the need for sophisticatedspectroscopy equipment (for example detecting absorption) that can bedifficult to implement and maintain in field conditions where thisapparatus is required

The at least one reagent may include a molybdate solution and a luminolsolution.

It is thus a feature of at least one embodiment of the invention toprovide a chemiluminescence reaction providing sufficient detectionlimits for airborne silica monitoring.

The at least one reagent may provide a buffer for bringing a pH of asilica in solution in the reagent tank within the range of 9 to 11before or simultaneous to the addition of the molybdate.

It is thus a feature of at least one embodiment of the invention toprovide improved sensitivity of the detection system throughoptimization of reagent pH.

The reagent reservoir or other mixing volume may provide for reflectingsurfaces for directing chemiluminescence from the reaction volume to thephotodetector. The photodetector may be a photomultiplier tube and mayadditionally incorporate photon counting electronics.

It is thus a feature of at least one embodiment of the invention toenhance the sensitivity of the detection system buying placement of themeasurement signal.

The airborne silica detection may further include a sensor sensing anamount of air received by the reagent tank from the particle growthchamber and providing the signal to the electronic computer forcomputing silica concentrations.

It is thus a feature of at least one embodiment of the invention toallow normalization of the measurements to varying amounts of air thatmay be collected by the system to provide a consistent standardizedoutput.

The airborne silica detection system may further include a filter forremoving ozone from the airstream before introduction into the reactionchamber. The filter for example may provide services coated withmaterials reacting with ozone

It is thus a feature of at least one embodiment of the invention toreduce or eliminate the effect of side reactions of thechemiluminescence materials with trace atmospheric gases such as ozone.

The particle growth chamber may provide a humidifier creating moistureto the particle growth chamber for condensing on the particles toincrease their mass.

It is thus a feature of at least one embodiment of the invention toprovide a simple method of increasing the interaction between extremelyfine particles and the reagent materials by increasing the mass of theparticles for improved integration into the reagent.

The humidifier may be a steam generator.

It is thus a feature of at least one embodiment of the invention toprovide a simple method of promoting particle size mass increase throughuse of fine particles as nucleation sites for saturated moisture.

The particle sizer may provide a cyclonic filter for selectivelyremoving particles greater than 4 μm in diameter and passing otherparticles to the particle growth chamber.

It is thus a feature of at least one embodiment of the invention toprovide a particle sizing device which can provide effective eliminationof particles unlikely to be associated with chronic respiratory diseasesbefore they undergo reaction and subsequent measurement.

The airborne silica detection may include a cartridge providing at leasttwo compartments holding reagents for use in the reagent tank and atleast one compartment for receiving waste reagent from the reagent tankand the airborne silica detection system may provide pumps controlled bythe controller for moving the reagents and waste to and from the reagenttank respectively.

It is thus a feature of at least one embodiment of the invention toprovide an effective method of managing cleaning the reagent tank in thefield in order to implement multiple automatic measurement cyclesthrough the use of replaceable prefilled cartridges.

The cartridge may further provide a compartment receiving particlesfiltered by the particle filter collected from the particle filter.

It is thus a feature of at least one embodiment of the invention toprovide for a simple disposal and sequestration mechanism for filteredparticles that can reduce interference in subsequent measurements.

The cartridge may further provide at least one compartment holdingrinsing water and for receiving wastewater and the airborne silicadetection system may further provide a rinse line providing water fromthe cartridge to the reagent tank and a drain line moving liquid fromthe reagent tank to the cartridge and wherein the electronic computerexecutes the stored program to automatically drain and rinse the reagenttank for repeated measurements.

It is thus a feature of at least one embodiment of the invention topermit automatic cleaning of the reagent tank in between used to permitmultiple successive measurements on a near real-time basis.

These particular objects and advantages may apply to only someembodiments falling within the claims and thus do not define the scopeof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a monitoring station using the presentinvention positioned in the path of generated dust;

FIG. 2 is a block diagram of the present invention showing the variouscomponents as controlled by a microcontroller;

FIG. 3 is a flowchart showing the principal steps of an exemplaryprogram executed by the microcontroller in one embodiment the presentinvention; and

FIG. 4 is a block diagram of a variant of the present invention showingthe various components as controlled by a microcontroller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, the present invention provides an on-site,real-time silica dust monitoring system 10 that may be used indoors, forexample, attached to the air circulation equipment of the building, oroutdoors, for example, placed in the flow path 16 of air passing throughdust-generating activities such as mining or the like (as shown). Themonitoring system 10 may provide for a housing 12 having an air samplinginlet 14 positioned in the dust flow path 16. The monitoring system 10may receive electrical power, for example, through power lines 18 andmay communicate data through a network connection 20 or wirelessly asdiscussed below.

Referring now to FIG. 2, the air sampling inlet 14 may lead to a cycloneseparator 22 of conventional design performing a size selection on theparticles in received air based on a defined cutpoint that allowspassage of smaller particles and rejection/collection of largerparticles. In an example with a cutpoint of 4 microns, cyclone separator22 preferentially rejecting particles larger than 4 microns into a wastecollection hopper 24 and allowing air holding particles of smaller sizeto pass through flow tube 26. Desirably, the cyclone separator 22 willallow passage of particles having an average diameter in a range from0.1 to 4 μm and will reject 70% of particles larger than 4 μm andpreferably 90% of the particles larger than 5 μm.

Air and dust particles from the flow tube 26 are received by a diffusiondenuder 28, providing a denuder tube 30 through which the air and dustparticles may pass to eliminate gaseous oxidizers that could affect thechemical reaction to be performed downstream as will be described. Thedenuder tube 30 may be heated by a heater 33 to promote reaction betweengases in the air and the tube walls (the latter, for example, beingcoated with potassium iodide, manganese dioxide or using heated copperor an ionic liquid coating such as [O35LUT⁺]). In one example, thedenuded tube 30 operates to filter out ozone and/or other oxidizinggases.

Air and dust particles exiting the diffusion denuder 28 may thenoptionally passed into a steam jet aerosol particle growth system 32providing a supersaturated steam atmosphere 34 produced by a steamgenerator 38. Smaller particles much less than four microns serve asnucleation sites for the supersaturated steam which condenses onto theirsurface, increasing the mass of fine particles and increasing theircollection within the reaction chamber 40 and interaction with thereagents contained therein. In this regard, the increased mass of theparticles tends to prevent them from percolating out of the solutionbefore reaction and the condensed water coating may increase theirmasses and thus integration into the collection reagent.

An outlet from the steam jet particle growth system 32 passes through animpinger tube 42 extending vertically downward into the reaction chamber40 to a point beneath the surface of a reaction medium 44 (being anaqueous solution of reactants to be described below) in the reactionchamber 40 serving to retain the dust particles as air and dustparticles bubble through the reaction medium 44 to exit an exhaust port46 in a wall of the reaction chamber 40 drawn by air pump 48. The outletof air pump 48 may provide for a flowmeter 50 so that a predeterminedvolume of air and particulates can be percolated through the reactionmedium 44 for each given measurement. Generally, the flowmeter 50 may bea mass flowmeter or may be a volume flowmeter with pressure gaugeintended to provide an approximation of the total mass of airstreamreceived by the reaction medium 44.

The reaction chamber 40 provides introduction ports 52 connected throughrespective pumps 54 a, 54 b, and 54 c (for example, peristaltic pumps)with corresponding water container 56 a and reagent reservoirs 56 b and56 c so that water and reagents can be introduced into the reactionchamber 40.

A drain pump 58 may communicate with the bottom of the reaction chamber40 to drain liquid from that reaction chamber 40 into a waste receptacle60.

The reaction chamber 40 may include a window and associated collectionoptics, for example, a collection lens and filter 62 and opposingreflector 65, to collect light within the volume of the reaction medium44 for measurement by a photomultiplier 64. In this way, silica in thereaction medium 44 may react with the reagents from reservoirs 56 b and56 c, and the light so produced may be measured for determination of themass of silica. The reflector 65 may be a discrete mirror or the entirereaction chamber 40 may be reflective in a way intending to collectlight for receipt by the photo multiplier 64. The filter may have abandpass characteristic centered around the frequency of the chemicalluminescence (e.g. 445 nanometers) to reject external light.Alternatively, or in addition, the reaction chamber 40 may be sealedagainst light.

Each of the heater 33, the steam generator 38, the air pump 48, the massflowmeter 50, the pumps 54 and 58, and the photomultiplier 64 maycommunicate with an electronic controller 70 providing a processor 72that may execute a stored program 74 contained in computer memory 76 aswill be discussed below. The controller 70 may also include interfacecircuitry, for example, an A/D converter or counter associated with thephotomultiplier 64 and various solid-state relays or switches forcontrolling power to the various other components described.

The controller 70 may communicate with signal lines 78 which may connectto a network or to a wireless communication device 80 for communicationof data to and from the controller 70.

Referring now to also to FIG. 3, the program 74 may operate to prepareto collect a sample of air and dust as indicated by process block 81.This process involves heating up the heater 33 (if used) and the steamgenerator 38 (if used) and filling the reaction chamber 40 with apredetermined volume of aqueous reagents using pump 54 b.

Once proper conditions have been obtained, the air pump 48 is activatedfor a period of time to draw a predetermined volume of air through thesystem to begin the collection of an air sample as indicated by processblock 82. The predetermined volume of air may be determined by measuringthe actual mass or volume of air to draw a predetermined amount airthrough the system using the flowmeter 50.

Particles sized in the cyclone separator 22 are drawn by the air pump48, through the diffusion denuder 28 to remove gaseous interferences andinto the steam jet particle growth chamber 34, followed by particlecollection and subsequent reaction in the reagent liquid by means of theimpinger 42. A sampling cycle, for example, may involve between 20minutes to one hour of sampling time at five liters per minute airflow.

After the air and dust sample has been completed, the air pump 48 may beturned off. At this point, as indicated by process block 84, reagentsmay be added to the reaction medium 44 using pumps 54 b and 54 c topromote chemiluminescence in proportion to the silica contained in thesampled air volume.

In particular, the reaction medium 44 in reservoir 56 b during thecollection of the air sample of process blocks 62 may be a molybdatesolution that combines with the silica to form a heteropoly acid (HPA).The HPA is then reduced using the reagent in container 56 c (addedduring process block 84) which may be a luminol solution(3-Aminophthalhydrazide, 5-Amino-3-dihydro-1, 4-phthalazinedione) whichreacts with the HPA to produce a quantitative amount of light at 445nanometers. The result is a chemical luminescence that can be used toderive a mass of silica involved in the reaction. The inventors havedetermined that sensitivity can be increased by control of the pH of thesolution receiving the silica to a value of 10 and ideally within arange from 9 to 11 before the introduction of the molybdate. Theinventors have determined that the limit of detection for silicate isapproximately 30 ng with a signal to noise ratio of four.

As indicated by process block 86, light received from the reactionmedium 44 by the photomultiplier 64 may be integrated, for example, fora predetermined time interval after the introduction of the reagents oraccording to threshold levels based on the maximum light output during apredetermined period. This integrated value is then provided to thecontroller 70 which may, for example, apply the empirically derivedtable to the measurement to output the total mass of silica within theair sample for the particular sensitivity of the photomultiplier 64 andthe optical system. Preferably, the signal from the photomultiplier 64and knowledge of the airflow mass from sensor 50 are used to establish adensity of SiO₂ within the air to provide an alarm if this densityexceeds 50 μg /m³ or over 25 μg/m³. As indicated by process block 88,this information may immediately be reported or may form the basis ofalarm or may implement automatic control measures, for example,increasing air filtration for indoor locations or introducing freshfiltered air into an interior workspace. During this reporting process,pump 58 may be activated to flush the reaction chamber 40 in preparationfor the next measurement. An additional water rinse of the reactionchamber 40 may then be performed to remove trace amounts of the silicaand reactants, using for example, water in an additional reservoir 56 a

Referring again to FIG. 2, each of the reservoirs 56 and 60 and wastecollection hopper 24 may be integrated into a single container toprovide a ready replacement of the consumables and disposal of the wasteof this process. Alternatively, separate containers may he provided forthe consumables and the waste material. A sensor 100 may detect thepresence of the container and/or levels of liquid in the container toprovide the controller 70 with information about the same. Referring toprocess block 90 of FIG. 3, at the conclusion of each measurement cycle,sensors 100 may be interrogated to provide information about the need toreplace any consumables or to empty the waste collection hopper 24 orreceptacle 60. Following these steps, the program 74 may loop back tostep 82 in order to monitor the air quality in a semi-continuous manner.

Referring now to FIG. 4, in another example, the real-time silica dustmonitoring system 10 is configured to continuously monitor the airquality. This real-time silica dust monitoring system 10 issubstantially similar to that shown in FIG. 2, only differs in thefollowing ways in order to achieve continuous monitoring. A virtualimpactor 110 and an air pump shown as vacuum pump 112 are incorporateddownstream of the cyclone separator 22 instead of diffusion denuder 28.The virtual impactor 110 performs a second stage of size selection, withthe cyclone separator's 22 cutpoint corresponding to the first stage ofsize selection and the virtual impactor's 110 cutpoint corresponding tothe second stage of size selection. Two exit tribes 114, 116 extend fromthe virtual impactor 110 and separate the gas flow of the virtualimpactor into a major flow that is removed through exit tube 114 by thevacuum pump 112 and a minor flow that flows through exit tube 116 andcontinues downstream through the real-time silica dust monitoring system10. Within the virtual impactor 110, particles with diameters greaterthan the virtual impactor's 110 cutpoint are entrained in and flow withthe minor flow whereas the particles with diameters that are smallerthan virtual impactor's 110 cutpoint along with the remainder of theflowing gas define the major flow that are pulled into the vacuum pump112. By incorporating the virtual impactor 110 the diffusion denuder 18may be eliminated as unnecessary in this example because the relativeconcentration of gaseous oxidizers will be reduced as the particleconcentration is increased. Furthermore, concentration the particles bya factor of up to a multiple of 10 may be achieved by the splitting andreduction of the gas flow. In this way, the combination of the cycloneseparator 22 and the virtual impactor 110 selects a “slice” of particlesof interest: those small enough to be respirable and those large enoughto substantially contribute to the silica mass.

Still referring to FIG. 4, instead of an impinger tube 42, an aerosolcollector 118 is provided, such as an Aerosol Counterflow Two-Jet Unit(ACTJU) aerosol collector, developed by Pavel Mikuška at the instituteof Analytical Chemistry of the Academy of Sciences in the CheckRepublic. In the aerosol collector 118, airborne particles aretransferred continuously into a small flow rate of water or otheraqueous solution from a solution delivery inlet 120. A reagent flowmixer 122 that receives reagent through a reagent inlet 124, a mixingtube shown as helical mixing tube 126, a heater 128, and luminol reagentmixer 130 that receives a luminol reagent through reagent inlet 132 arearranged downstream of the aerosol collector 118 and upstream of areaction flow cell 134. Reaction flow cell 134 has a window andassociated collection optics, which may be similar to those shown inFIG. 2 and may include a reflective surface of the reaction flow cell134 or a reflector 65, collection lens and filter 62, photomultipliertube such as photomultiplier 64, along with photon counting electronics,which include various photon counting units and other photon countingproducts available from, for example, Hamamatsu Photonics, BostonElectronics, or the like.

Still referring to FIG. 4, after the airborne particles are transferredcontinuously into the small flow of water or other aqueous solution inthe aerosol collector 118, it flows into the reagent flow mixer 122 tomix with the reagent from reagent inlet 124. The first reagent mixedwith the aerosol collector's 118 liquid flow in the reagent flow mixer122 is a molybdate solution that combines with silica at an appropriatepH to form an HPA (heteropoly acid), which then flows into the helicalmixing tube 126. The reaction occurring in the helical mixing tube 126is performed for an optimized period of time determined by the flow rateof liquid through the aerosol collector 118 and the length of thehelical mixing tube 126. The mixed liquid/reagent flow passing throughthe helical mixing tube 126 flows at a rate that provides a residencetime within the helical mixing tube 126 that is adequate to complete thereaction. The temperature of this reaction may also be controlled by wayof heater 128 to ensure completion of the reaction. This fully reactedmixture exits the helical mixing tube 126 and flows into the luminolreagent mixer 130 to mix with a chemiluminescence or luminol reagent.Accordingly, in the luminol reagent mixer 130, the HPA is subsequentlyreduced by mixing with the luminol reagent, such as3-Aminophthalhrydrazide, 5-Amino-2, 3-dihydro-1, 4-phthalazinedione,which is delivered through reagent inlet 132 and reacts with the HPA toproduce a quantitative amount of light at, for example, 445 nanometers.Because this reaction is rapid, this mixing is done or completed in thereaction flow cell 134 that is viewed by the light detection systemincorporating photomultiplier tube 64 and photon counting electronics.In the flow cell 134, the light produced may be collected by way of thephoton counting electronics and completely and measured for thedetermination of the mass of silica.

Still referring to FIG. 4, in this example of a continuously operatingreal-time silica dust monitoring system 10, particles are continuouslytransferred and concentrated into solution so that they are undergoingchemical transformations to produce light continuously rather than inbatches. Instead of accumulating particles in suspension prior to batchchemical reaction like described with respect to FIG. 2, the chemicalreaction occurs continuously, and the photon counts (light) isaccumulated electronically. Since continuous measurements are made inthis example, the air and reaction solutions are correspondingly pumpingcontinuously. No airflow amounts need to be determined since theinstrument(s) sense how often it may report a value based on thesignal-to-noise ratio as photon counts accumulate. Nor is rinsing orflushing required for subsequent measurements due to the continuousnature of the measurement. The virtual impactor 110 and the capture ofparticles into the liquid phase can be done efficiently in a muchsmaller volume compared to the system shown in FIG. 2. Although theresponse time should not be substantially altered, the system of FIG. 4can allow for more easily variable control because the photons resultingfrom the chemistry are counted continuously. Thus, the instrumentcontrol system can determine how long to collect light in order to havean adequate signal-to-noise ratio to insure quantification of silicaparticles. Due to the continuous nature of the measurement, theinstrumentation may be simpler than in systems that require time-varyingcontrol procedures intrinsic to batch mode measurements.

Certain terminology is used herein for purposes of reference only, andthus is not intended to be limitinge. For example, terms such as“upper”, “lower”, “above”, and “below” refer to directions in thedrawings to which reference is made. Terms such as “front”, “back”,“rear”, “bottom” and “side”, describe the orientation of portions of thecomponent within a consistent but arbitrary frame of reference which ismade clear by reference to the text and the associated drawingsdescribing the component under discussion. Such terminology may includethe words specifically mentioned above, derivatives thereof, and wordsof similar import. Similarly, the terms “first”, “second” and other suchnumerical terms referring to structures do not imply a sequence or orderunless clearly indicated by the context.

When introducing elements or features of the present disclosure and theexemplary embodiments, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of such elements orfeatures. The terms “comprising”, “including” and “having” are intendedto be inclusive and mean that there may be additional elements orfeatures other than those specifically noted. It is further to beunderstood that the method steps, processes, and operations describedherein are not to be construed as necessarily requiring theirperformance in the particular order discussed or illustrated, unlessspecifically identified as an order of performance. It is also to beunderstood that additional or alternative steps may be employed.

References to “a microprocessor” and “a processor” or “themicroprocessor” and “the processor,” can be understood to include one ormore microprocessors that can communicate in a stand-alone and or adistributed environment(s), and can thus be configured to communicatevia wired or wireless communications with other processors, where suchone or more processor can be configured to operate on one or moreprocessor-controlled devices that can be similar or different devices.Furthermore, references to memory, unless otherwise specified, caninclude one or more processor-readable and accessible memory elementsand/or components that can be internal to the processor-controlleddevice, external to the processor-controlled device, and can be accessedvia a wired or wireless network.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein and the claims shouldbe understood to include modified forms of those embodiments includingportions of the embodiments and combinations of elements of differentembodiments as come within the scope of the following claims. All of thepublications described herein, including patents and non-patentpublications, are hereby incorporated herein by reference in theirentireties.

What we claim is:
 1. An airborne silica detection system comprising: aparticle sizer for receiving an airstream and preferentially removingparticles greater than 4 μm average diameter from the airstream; areagent tank receiving the airstream downstream from the particle sizerand introducing it into a at least one liquid reagent reacting withsilica of the particles; a photodetector monitoring the reagent tank todetect a change in light caused by the reacting of the silica; and anelectronic computer executing a stored program held in non-transitorycomputer readable medium to receive a signal from the photo detector toprovide an output indicating silica concentrations over a predeterminedamount.
 2. The airborne silica detection system of claim 1 furtherincluding a particle growth chamber receiving the airstream from theparticle sizer to increase the individual mass of the particles lessthan 4 μm in diameter prior to receipt by the reagent tank.
 3. Theairborne silica detection system of claim I wherein the predeterminedamount is a density of silicon dioxide of less than 0.1 μg/m³ in theairstream.
 4. The airborne silica detection system of claim 3 whereinthe predetermined amount is a density of silicon dioxide less than 40μg/m³ in the airstream.
 5. The airborne silica detection system of claim2 wherein the at least one reagent provide a chemiluminescent reactionand the photodetector is a light sensor directed into the reagent tank.6. The airborne silica detection system of claim 5 wherein the at leastone reagent include a molybdate solution and a luminol solution.
 7. Theairborne silica detection system of claim 6 wherein the at least onereagent provide a buffer for bringing a pH of a silica in solution inthe reagent tank within the range of 9 to 11 before the addition of themolybdate.
 8. The airborne silica detection system of claim 5 whereinthe reagent tank provides for reflecting surfaces for directingchemiluminescence from the reagent to the photodetector.
 9. The airbornesilica detection system of claim 8 wherein the photodetector is aphotomultiplier tube.
 10. The airborne silica detection system of claim1 further including a sensor sensing an amount of air received by thereagent tank from the particle growth chamber and providing the signalto the electronic computer for computing silica concentrations.
 11. Theairborne silica detection system of claim 1 further including filter forremoving ozone from the airstream before introduction into the reactionchamber.
 12. The airborne silica detection system of claim 11 whereinthe filter provides surfaces coated with materials reacting with ozone.13. The airborne silica detection system of claim 1 wherein the particlegrowth chamber provides a humidifier providing moisture to the particlegrowth chamber for condensing on the particles to increase their mass.14. The airborne silica detection system of claim 13 wherein theparticle growth chamber provides a humidifier providing moisture to theparticle growth chamber for the humidifier is a steam generator.
 15. Theairborne silica detection system of claim 1 wherein the particle sizeris a cyclonic filter for selectively removing particles greater than 4μm in diameter and passing other particles to the particle growthchamber.
 16. The airborne silica detection system of claim 1 furtherincluding a cartridge providing at least two compartments holdingreagents for use in the reagent tank and at least one compartment forreceiving waste reagent from the reagent tank and wherein the airbornesilica detection system provides pumps controlled by the controller formoving the reagents and waste to and from the reagent tank respectively.17. The airborne silica detection system of claim 1 wherein thecartridge further provides a compartment receiving particles filtered bythe particle filter collected from the particle filter.
 18. The airbornesilica detection system of claim 1 wherein the cartridge furtherprovides at least one compartment holding rinsing water and forreceiving wastewater and further including a rinse line providing waterfrom the cartridge to the reagent tank and a drain line moving liquidfrom the reagent tank to the cartridge and wherein the electroniccomputer executes the stored program to automatically drain and rinsethe reagent tank for repeated measurements.